1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens. The embodiments described herein are considered suitable for, for example, image pickup apparatuses including image pickup devices, such as a digital still camera, a video camera, a monitoring camera, and a broadcast camera, or image pickup apparatuses such as a silver-halide-film camera.
2. Description of the Related Art
Recent image pickup apparatuses including solid-state image pickup devices, such as a digital still camera and a video camera, have improved functions while the total sizes thereof are reduced. Zoom lenses intended for such apparatuses are desired to have short total lengths and high magnifications. To meet such demands, a known positive-lead, four-unit zoom lens includes lens units having positive, negative, positive, and positive refractive powers, respectively, in that order from an object side to an image side thereof.
Japanese Patent Application Laid-Open No. 2007-264390 discloses a zoom lens including low-cost lens elements and in which all lens units are moved during zooming while the distance between adjacent ones of the lens units is set appropriately. In the zoom lens according to Japanese Patent Application Laid-Open No. 2007-264390, a first lens unit consists of a positive lens element and a negative lens element, a third lens unit includes a plastic lens element, and the refractive power of the third lens element is set appropriately, whereby the thicknesses of the lens units are reduced. Thus, a high-magnification, low-cost zoom lens is provided.
Japanese Patent Application Laid-Open No. 2009-163102 discloses a zoom lens in which all lens units are moved during zooming while the distance between adjacent ones of the lens units is set appropriately. By appropriately setting the distance between adjacent ones of the lens units, aberrations that tend to occur around the image field during zooming are reduced. Thus, a high-magnification, compact zoom lens is provided.
In general, to provide a high-magnification imaging optical system, the refractive powers of the respective lens units included in the imaging optical system are increased while the distance between adjacent ones of the lens units are set appropriately. However, if the lengths of travel of the lens units during zooming are increased, the total length of the zoom lens may increase. As stated above, an increased total length of the zoom lens is not desirable.